Generally, in a gas turbine generating facility, the amount of fuel supply to a gas turbine is controlled such that generator output follows a demand load of a utility grid. For example, PTL 1 discloses adjusting generator output by controlling a degree of opening of a fuel control valve, and causing the generator output to follow a demand load, by inputting a deviation of the generator output with respect to a generator output set value (LDSET) set based on the demand load of a utility grid into a PI controller and performing proportional integral calculation based on this deviation.